This invention relates to fuel effectiveness in energy conversion. More particularly, it pertains to a method and apparatus for the generation of heat energy and cooling capacity by mechanical means, at temperatures suitable for industrial and residential applications and at a fuel effectiveness substantially higher than the heating value of the fuel consumed.
A substantial part of world-wide fuel consumption is devoted to providing heat energy for industrial, commercial and residential purposes in the temperature range up to 400.degree. C. Mostly, this heat is still generated in essentially the same manner since ancient times, namely by burning fuel. Even if the most elaborate methods of heat recovery are employed, the outcome of this direct approach to heat generation can never exceed the thermal equivalent of the fuel consumed, as a theoretical upper limit.
While the procedure of burning fuel directly for heat generation was sufficiently sophisticated as long as fuel was abundant and cheap, it is no longer the case. With growing awareness of this fact, alternate methods of heat energy generation have been proposed to conserve scarce fuel.
For example, U.S. Pat. No. 3,962,873 issued to J. P. Davis on June 15, 1976 discloses a process in which water is first converted to steam in the range of 65.degree.-120.degree. C. and a corresponding pressure range of roughly 0.25-2.0 bar by means of solar collectors, and then the low pressure steam is compressed mechanically to higher pressures and temperatures suitable for industrial applications.
Though the prime-mover/compressor of the Davis system has a combined efficiency of only about 30-35 percent, additional high pressure steam can be generated from the otherwise reject heat of the engine exhaust and cooling water system to provide a total steam output, for example at approximately 4 bars and about 350.degree. C., that may be as much as three times the amount of steam that would be produced under comparable conditions by direct firing in a conventional boiler. This assumes, of course, that a substantial portion of the total heat input is supplied by solar energy.
In the example given in the patent, the solar contribution is about 65% of the total energy input. Thus, for periods when little or no solar flux is available, a fuel fired standby boiler is needed, and the fuel efficiency of the hybrid Davis process under such conditions becomes merely that of a conventional boiler.
Moreover, the Davis process follows the conventional approach to steam generation of heating an initial feed water flow, whether in a boiler or a solar collector, to convert the feed water into steam. This means that the initial feed supply must consist of relatively pure water to avoid fouling the heat transfer surfaces with deposits of impurities contained in the feed and left behind when the water boils to steam, unless the condensate is returned.
Furthermore, though the solar heating of the feed water causes an appropriately higher heat output, it is nevertheless expensive by reason of the high investment in solar collectors. A process which does not require preliminary heating of any kind for the feed water, but which can exploit the depleted heat energy inherent in the ambient feed water itself, can not only do away with the solar collectors but is also independent of available solar flux and able to operate day and night uninterruptedly in any weather without a boiler.
Throughout the world, moreover, there exist large water bodies which are too impure by nature or too polluted by men to be used directly in industrial processes or, for that matter, for human consumption, and large amounts of capital and fuel are spent to purify some of it, or at least to halt pollution. Much of this investment can be saved by a process which not only does not require feed water of boiler quality, but which even generates an output of pure water.
Examples of such ambient natural water bodies include lakes, rivers and the oceans, while man-made sources of constant supply and mostly elevated temperature include industrial effluents, municipal sewage, juices, beverages, etc.
One significant example of an above ambient temperature aqueous source is condensing water rejected from fossil fuel fired or nuclear power plants. This source at the present time is considered as a generator of thermal pollution and represents an important limiting factor in the increased use of nuclear energy.
Although the thermal energy potential in large aqueous bodies, such as the oceans, has been recogized, most proposals to extract this energy rely on significant temperature differences, such as between surface and deep ocean water, to provide a thermal potential for operating an evaporating/condensing power plant cycle using an intermediate working fluid. Any attempts to convert such aqueous sources directly into steam have been considered impractical because of the high cost of preliminary treatment to obtain boiler feed water of suitable purity.